The proliferation of smart amplifiers, dynamic gain equalizers and optical cross-connects has added tremendous functionality to current and next generation optical networks. These intelligent WDM networks require performance or channel monitors to monitor the spectrum of the optical channels, including channel power and channel identification. This spectrum information is particularly valuable considering the frequency at which the optical channels dynamically change.
Conventional network monitors, such as optical spectrum analyzers OSAs, provide comprehensive channel information, however OSAs are expensive, bulky and provide more capabilities or features than necessary for a telecommunications network.
One such OSA is shown in U.S. Pat. No. 5,233,405 entitled “Optical Spectrum Analyzer Having Double Pass Monochromator”. The optical spectrum analyzer includes double pass monochromator that has an input optical fiber for emitting a light beam, a diffraction grating for diffracting the input light beam to produce a spatially dispersed light beam, a slit for passing a selected portion of the dispersed light beam and an output optical fiber. A motor rotates the diffraction grating to detected each of the optical channels or wavelength bands. The position of the grating is sensed by a shaft encoder.
A similar double pass monochromator is shown in U.S. Pat. No. 6,166,805, entitled “Double Pass Monochromator”. The monochromator includes a diffraction means, a pair of concave mirrors, a return reflection means, a photodetector and a plurality of slits. The diffraction grating pivots about an axis of rotation.
Besides OSAs based on free space optics, grating-based channel monitors are known. One such channel monitor is shown in U.S. Pat. No. 5,995,255, entitled “Concatenated Fiber Grating Optical Monitor”. The monitor is a wavelength division multiplexing (WDM) optical monitor, based on concatenated fiber gratings, that uses a modulator and detector.
What is needed is a small, inexpensive optical spectral analyzer that provides an output signal indicative of the spectral profile of the optical input signal.